697 research outputs found
Discovery of A New Retrograde Trans-Neptunian Object: Hint of A Common Orbital Plane for Low Semi-Major Axis, High Inclination TNOs and Centaurs
Although the majority of Centaurs are thought to have originated in the
scattered disk, with the high-inclination members coming from the Oort cloud,
the origin of the high inclination component of trans-Neptunian objects (TNOs)
remains uncertain. We report the discovery of a retrograde TNO, which we
nickname "Niku", detected by the Pan-STARRS 1 Outer Solar System Survey. Our
numerical integrations show that the orbital dynamics of Niku are very similar
to that of 2008 KV (Drac), with a half-life of Myr. Comparing
similar high inclination TNOs and Centaurs ( AU, ), we find that these objects exhibit a surprising clustering of
ascending node, and occupy a common orbital plane. This orbital configuration
has high statistical significance: 3.8-. An unknown mechanism is
required to explain the observed clustering. This discovery may provide a
pathway to investigate a possible reservoir of high-inclination objects.Comment: 18 pages, 4 figures, 1 table, accepted for publication in ApJ Letter
Policy Feedback and the Politics of the Affordable Care Act
There is a large body of literature devoted to how âpolicies create politicsâ and how feedback effects from existing policy legacies shape potential reforms in a particular area. Although much of this literature focuses on selfâreinforcing feedback effects that increase support for existing policies over time, Kent Weaver and his colleagues have recently drawn our attention to selfâundermining effects that can gradually weaken support for such policies. The following contribution explores both selfâreinforcing and selfâundermining policy feedback in relationship to the Affordable Care Act, the most important healthâcare reform enacted in the United States since the midâ1960s. More specifically, the paper draws on the concept of policy feedback to reflect on the political fate of the ACA since its adoption in 2010. We argue that, due in part to its sheer complexity and fragmentation, the ACA generates both selfâreinforcing and selfâundermining feedback effects that, depending of the aspect of the legislation at hand, can either facilitate or impede conservative retrenchment and restructuring. Simultaneously, through a discussion of partisan effects that shape Republican behavior in Congress, we acknowledge the limits of policy feedback in the explanation of policy stability and change
The Pan-STARRS Moving Object Processing System
We describe the Pan-STARRS Moving Object Processing System (MOPS), a modern
software package that produces automatic asteroid discoveries and
identifications from catalogs of transient detections from next-generation
astronomical survey telescopes. MOPS achieves > 99.5% efficiency in producing
orbits from a synthetic but realistic population of asteroids whose
measurements were simulated for a Pan-STARRS4-class telescope. Additionally,
using a non-physical grid population, we demonstrate that MOPS can detect
populations of currently unknown objects such as interstellar asteroids.
MOPS has been adapted successfully to the prototype Pan-STARRS1 telescope
despite differences in expected false detection rates, fill-factor loss and
relatively sparse observing cadence compared to a hypothetical Pan-STARRS4
telescope and survey. MOPS remains >99.5% efficient at detecting objects on a
single night but drops to 80% efficiency at producing orbits for objects
detected on multiple nights. This loss is primarily due to configurable MOPS
processing limits that are not yet tuned for the Pan-STARRS1 mission.
The core MOPS software package is the product of more than 15 person-years of
software development and incorporates countless additional years of effort in
third-party software to perform lower-level functions such as spatial searching
or orbit determination. We describe the high-level design of MOPS and essential
subcomponents, the suitability of MOPS for other survey programs, and suggest a
road map for future MOPS development.Comment: 57 Pages, 26 Figures, 13 Table
23 High Redshift Supernovae from the IfA Deep Survey: Doubling the SN Sample at z>0.7
We present photometric and spectroscopic observations of 23 high redshift
supernovae spanning a range of z=0.34-1.03, 9 of which are unambiguously
classified as Type Ia. These supernovae were discovered during the IfA Deep
Survey, which began in September 2001 and observed a total of 2.5 square
degrees to a depth of approximately m=25-26 in RIZ over 9-17 visits, typically
every 1-3 weeks for nearly 5 months, with additional observations continuing
until April 2002. We give a brief description of the survey motivations,
observational strategy, and reduction process. This sample of 23 high-redshift
supernovae includes 15 at z>0.7, doubling the published number of objects at
these redshifts, and indicates that the evidence for acceleration of the
universe is not due to a systematic effect proportional to redshift. In
combination with the recent compilation of Tonry et al. (2003), we calculate
cosmological parameter density contours which are consistent with the flat
universe indicated by the CMB (Spergel et al. 2003). Adopting the constraint
that Omega_total = 1.0, we obtain best-fit values of (Omega_m,
Omega_Lambda)=(0.33, 0.67) using 22 SNe from this survey augmented by the
literature compilation. We show that using the empty-beam model for
gravitational lensing does not eliminate the need for Omega_Lambda > 0.
Experience from this survey indicates great potential for similar large-scale
surveys while also revealing the limitations of performing surveys for z>1 SNe
from the ground.Comment: 67 pages, 12 figures, 12 tables, accepted for publication in the
Astrophysical Journa
Eight-Dimensional Mid-Infrared/Optical Bayesian Quasar Selection
We explore the multidimensional, multiwavelength selection of quasars from
mid-IR (MIR) plus optical data, specifically from Spitzer-IRAC and the Sloan
Digital Sky Survey (SDSS). We apply modern statistical techniques to combined
Spitzer MIR and SDSS optical data, allowing up to 8-D color selection of
quasars. Using a Bayesian selection method, we catalog 5546 quasar candidates
to an 8.0 um depth of 56 uJy over an area of ~24 sq. deg; ~70% of these
candidates are not identified by applying the same Bayesian algorithm to
4-color SDSS optical data alone. Our selection recovers 97.7% of known type 1
quasars in this area and greatly improves the effectiveness of identifying
3.5<z<5 quasars. Even using only the two shortest wavelength IRAC bandpasses,
it is possible to use our Bayesian techniques to select quasars with 97%
completeness and as little as 10% contamination. This sample has a photometric
redshift accuracy of 93.6% (Delta Z +/-0.3), remaining roughly constant when
the two reddest MIR bands are excluded. While our methods are designed to find
type 1 (unobscured) quasars, as many as 1200 of the objects are type 2
(obscured) quasar candidates. Coupling deep optical imaging data with deep
mid-IR data could enable selection of quasars in significant numbers past the
peak of the quasar luminosity function (QLF) to at least z~4. Such a sample
would constrain the shape of the QLF and enable quasar clustering studies over
the largest range of redshift and luminosity to date, yielding significant
gains in our understanding of quasars and the evolution of galaxies.Comment: 49 pages, 14 figures, 7 tables. AJ, accepte
Imaging and spectroscopy of arcs around the most luminous X-ray cluster RX J1347.5-1145
The cluster RX J1347.5-1145, the most luminous cluster in the X-ray
wavelengths, was imaged with the newly installed Space Telescope Imaging
Spectrograph (STIS) on-board HST. Its relatively high redshift (0.451) and
luminosity indicate that this is one of the most massive of all known clusters.
The STIS images unambiguously show several arcs in the cluster. The largest two
arcs (> 5 arcsec in length) are symmetrically situated on opposite sides of the
cluster, at a distance of ~ 35 arcsec from the central galaxy. The STIS images
also show approximately 100 faint galaxies within the radius of the arcs whose
combined luminosity is ~ 4 x 10^11 Lsun. We also present ground-based
spectroscopic observations of the northern arc which show one clear emission
line at 6730 A, which is consistent with an identification as [OII] 3727 A,
implying a redshift of 0.81 for this arc. The southern arc shows a faint
continuum but no emission features. The surface mass within the radius of the
arcs (240 kpc), as derived from the gravitational lensing, is 6.3 x 10^14 Msun.
The resultant mass-to-light ratio of ~1200 is higher than what is seen in many
clusters but smaller than the value recently derived for some `dark' X-ray
clusters (Hattori et al. 1997). The total surface mass derived from the X-ray
flux within the radius of the arcs is ~2.1 - 6.8 x 10^14 Msun, which implies
that the ratio of the gravitational to the X-ray mass is ~1 to 3. The surface
GAS mass within this radius is ~3.5 x 10^13 Msun, which implies that at least
6% of the total mass within this region is baryonic.Comment: 3 figures. Replaced with the final version as appears in the
Astrophysical Journal Letters (Jan 10, 1998 issue). This incorporates some
important revision
Comment on Spracklandus Hoser, 2009 (Reptilia, Serpentes, ELAPIDAE): request for confirmation of the availability of the generic name and for the nomenclatural validation of the journal in which it was published (Case 3601; see BZN 70: 234â237; 71: 30â38, 133â135, 181â182, 252â253)
A Risk Assessment Tool for Predicting Fragility Fractures and Mortality in the Elderly
Existing fracture risk assessment tools are not designed to predict fracture-associated consequences, possibly contributing to the current undermanagement of fragility fractures worldwide. We aimed to develop a risk assessment tool for predicting the conceptual risk of fragility fractures and its consequences. The study involved 8965 people aged >= 60 years from the Dubbo Osteoporosis Epidemiology Study and the Canadian Multicentre Osteoporosis Study. Incident fracture was identified from X-ray reports and questionnaires, and death was ascertained though contact with a family member or obituary review. We used a multistate model to quantify the effects of the predictors on the transition risks to an initial and subsequent incident fracture and mortality, accounting for their complex interrelationships, confounding effects, and death as a competing risk. There were 2364 initial fractures, 755 subsequent fractures, and 3300 deaths during a median follow-up of 13 years (interquartile range [IQR] 7-15). The prediction model included sex, age, bone mineral density, history of falls within 12 previous months, prior fracture after the age of 50 years, cardiovascular diseases, diabetes mellitus, chronic pulmonary diseases, hypertension, and cancer. The model accurately predicted fragility fractures up to 11 years of follow-up and post-fracture mortality up to 9 years, ranging from 7 years after hip fractures to 15 years after non-hip fractures. For example, a 70-year-old woman with aT-score of -1.5 and without other risk factors would have 10% chance of sustaining a fracture and an 8% risk of dying in 5 years. However, after an initial fracture, her risk of sustaining another fracture or dying doubles to 33%, ranging from 26% after a distal to 42% post hip fracture. A robust statistical technique was used to develop a prediction model for individualization of progression to fracture and its consequences, facilitating informed decision making about risk and thus treatment for individuals with different risk profiles. (c) 2020 American Society for Bone and Mineral Research
Reduced bone loss is associated with reduced mortality risk in subjects exposed to nitrogen bisphosphonates: A mediation analysis
Bisphosphonates, potent anti-resorptive agents, have been found to be associated with mortality reduction. Accelerated bone loss is, in itself, an independent predictor of mortality risk, but the relationship between bisphosphonates, bone loss, and mortality is unknown. This study aimed to determine whether the association between bisphosphonates and mortality is mediated by a reduction in the rate of bone loss. Participants from the populationâbased Canadian Multicentre Osteoporosis Study were followed prospectively between1996 and 2011. Comorbidities and lifestyle factors were collected at baseline and bone mineral density (BMD) at baseline and at years 3 (for those aged 40 to 60 years), 5, and 10. Rate of bone loss was calculated using linear regression. Information on medication use was obtained yearly. Bisphosphonate users grouped into nitrogen bisphosphonates (nBP; alendronate or risedronate) and etidronate and nonâusers (NoRx) were matched by propensity score, including all baseline factors as well as time of treatment. Coxâs proportional hazards models, unadjusted and adjusted for annual rate of bone loss, were used to determine the association between nBP and etidronate versus NoRx. For the treatment groups with signiïŹcant mortality risk reduction, the percent of mortality reduction mediated by a reduction in the rate of bone loss was estimated using a causal mediation analysis. There were 271 pairs of nBP and matched NoRx and 327 pairs of etidronate and matched NoRx. nBP but not etidronate use was associated with signiïŹcant mortality risk reduction (hazard ratios [HR]=0.61 [95% conïŹdenceinterval0.39â0.96]and1.35[95%CI0.86â2.11] for nBP and etidronate, respectively). Rapid bone loss was associated with more than2âfold increased mortality risk compared with no loss. Mediation analysis indicated that39% (95%CI7%â84%) of the nBP association with mortality was related to a reduction in the rate of bone loss. This ïŹnding provides an insight into the mechanism of the relationship between nBP and survival beneïŹt in osteoporotic patients
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